1. Field of the Invention
The present invention relates to a magnetic bubble memory device and, more particularly, to an improvement in arrangement of magnetic bubble detector and magnetic bubble generator relative to each other in the memory device of the kind mentioned above.
2. Description of the Prior Art
The magnetic bubble memory device has been well known to those skilled in the art. One mode of operation of such a memory device is called "field access". This is because the movement of the magnetic bubble in a film of bubble material is made in response to a drive field which rotates in the plane of the film.
In a typical case, the film is made of an epitaxial film of garnet. The magnetic bubble moves in the film along a propagation path which is determined by the periodic pattern of a magnetically soft element (high permeability), typically permalloy. This element produces a magnetic pole pattern in response to the drive field rotating in the plane of the film, which in turn forms a localized field gradient by which the magnetic bubble is moved.
This type of magnetic bubble memory device is usually constructed in the form of a "major-minor loops" organization. In the memory device of this type, as is well known, the information is written and read in and out of data block unit, and the time regions for writing and reading operations are completely separated from each other.
Recently, there has been proposed a block type replicator/transfer gate, as in the AIP Conference Proceedings No. 18 P100-104 (1974), P. I. Bonyhard et al., which conveniently affords a major line/minor loops organization. Consequently, it has become possible to easily effect the reading and writing operations in the same time region. Clearly, it is more advantageous to make the reading and writing operations in the same time region than in the separate time regions.
FIG. 1 shows an example of memory organization capable of performing the reading and writing, e.g. transfer-out and transfer-in, operations in the same time region. The magnetic bubble generated by a magnetic bubble generator 2 provided on a magnetic bubble memory chip 1 is moved along the transfer in major line 3, in response to a rotating magnetic field. As a data block in which the "presence" and "absence" of the magnetic bubble correspond to "1" and "0" of binary notation has reached each transfer-in gate 4 on the major line 3, the magnetic bubble is transferred to the minor loop 7, by a delivery of a pulse from a transfer pulse source 5 to a conductor 6. This is the theory of the transfer-in operation. The magnetic bubble on the minor loop 7 is recirculated along this loop in accordance with the rotating magnetic field.
As to the reading operation, when the address to be read out on the minor loop has reached a position corresponding to the transfer-out gate 9 of a major line 8, the magnetic bubble on the minor loop 7 is replicated and transferred to a major line 8, by a delivery of a replicating pulse from a replicate/transfer out pulse source 10 to a conductor 17. The magnetic bubble on the major line 8 is moved in response to the rotating magnetic field and finally reaches a magnetic bubble detector 11, where the "presence" or "absence" of the magnetic bubble is transformed into an electric signal corresponding to "1" or "0" of binary notation.
The rewriting operation for rewriting the information in an address on the minor loop 7 is conducted in the following manner. When the address on the minor loop 7 to be rewritten has reached the position corresponding to the transfer-out gate of the major line 8, the magnetic bubble on the minor loop 7 is transferred to the major line 8, as the transfer pulse coming from the replicate/transfer pulse source 10 is delivered to the conductor 17. As a result, this address on the minor loop 7 becomes a vacant address in which there is no magnetic bubble. The new information is written in this vacant address, as the latter is brought to the position corresponding to the transfer-in gate 4.
There are two cases of rewriting: the rewriting of the whole content of the block and a partial rewriting. In either case, the old information which has been read out from the minor loop 7 and transferred to the major line 8 is moved in accordance with the rotating magnetic field to the magnetic bubble detector 11, and is erased after a detection by the detector 11. The output of the detector 11 corresponding to the old information may be used as a confirmation and check. Particularly, when only a part of the content of the data block is to be rewritten, the detecting output from the magnetic bubble detector 11 is fed back to the magnetic bubble generator 2 which produces the same information as the fed back output, and the information is renewed only in the address to be rewritten.
Therefore, in order to shorten the time required for the rewriting, it is necessary to overlap the time regions for the transfer-out and transfer-in operations.
However, the magnetic bubble generator, which is usually of the nucleation type, produces a large amount of noise when the transfer-in and transfer-out operations are performed in the overlapped time regions, so as to adversely affect the detector 11. Consequently, the output from the magnetic bubble detector 11 involves a large amount of noise which makes it difficult to discriminate between the "presence" and "absence" of the magnetic bubble.